The subject matter disclosed herein relates to the art of rotary wing aircraft and, more specifically, to rotor systems for rotary wing aircraft.
In typical rotary winged aircraft, for example, helicopters, rotary power is transmitted from an engine through a gearbox into the rotor system. The gearbox includes a housing-mounted large diameter bull gear that drives a main rotor shaft which in turn drives a main rotor of the aircraft. During aircraft operations, however, flight loads on the main rotor causes misalignment and/or relative movement or deflection between the bull gear and the rotor shaft.
To accommodate the relative deflections, a complex system of parts is included to connect the bull gear to the main rotor shaft. Referring to FIG. 5, the first is an adapter 100. The adapter 100 is engaged to the main rotor shaft 102 via a spline 104 at its inner diameter and is fixed to the main rotor shaft 102 via a nut 116. Typically, due to their size and other factors such as material properties of the main rotor shaft 102, splines 104 on main rotor shafts 102 cannot be crowned, making this arrangement necessary. The adapter 100 has a second spline 106 at its outer diameter that is crowned to allow for the misalignment between the main rotor shaft 102 and the bull gear 108. The second component, a quill shaft 110 has a pair of splines separated by a considerable axial distance. One spline of the pair of splines, typically the lower spline 114, is crowned to accommodate the predicted misalignment. The upper spline 112 of the quill shaft 110 is an internal spline and mates with the adapter 100, while the lower spline 114 is an external spline and mates with the bull gear 108.
There are many disadvantages to such a system. First, the number and size of components results in a heavy assembly. Second, the height required, in particular by the quill shaft, increases assembly envelope and weight. Additionally, the assembly relies on crowned splines, which tend to exhibit wear issues in applications such as these. Finally, this system easily accommodates angular or circumferential misalignments relative to the main rotor axis, but has limited capability to accommodate radial deflection.